The present invention relates to a laminated heat exchanger adapted for use as an evaporator of a vehicular air conditioner.
FIG. 1 shows a conventional laminated heat exchanger used as an evaporator of a vehicular air conditioner. Referring to FIG. 1, air passages are defined in refrigerant tubes 1 through which a refrigerant flows, and air-side corrugated fines 2 are arranged in these air passages. The refrigerant tubes 1 and the corrugated fins 2 are arranged in layers, their respective top portions are connected to one another, and they all are integrally brazed together. In FIG. 1, numeral 3 denotes a flow of the refrigerant in the laminated heat exchanger, while numeral 4 designates an air current flowing through the air passages.
FIG. 2 is an exploded perspective view of one of the refrigerant tubes 1. A pair of molded plates 5a and 5b each have a shallow tray portion and deeper refrigerant tank sections 6 formed at one end thereof. The molded plates 5a and 5b are opposed and bonded to each other, thereby defining between them a U-shaped refrigerant passage 7 through which the refrigerant introduced through one of the tank sections 6 is delivered to the other tank section. Corrugated inner fins 8 are inserted in the passage 7. The inner fins 8 serve to enlarge the refrigerant-side heat transfer area, thereby improving the heat transfer performance.
FIG. 3 is a top plan view of the laminated heat exchanger, FIGS. 4 and 5 are sectional views taken along lines IV--IV and V--V, respectively, of FIG. 3. A refrigerant inlet header 9 is provided on the upper portion of one side face of the heat exchanger through which the refrigerant flows into the heat exchanger. A connecting hole 12 is bored through a side face portion of the header 9. The hole 12 is connected to an inlet port 10 in an endplate 11 by being fitted thereon. The port 10, which is bored through the endplate 11, is an inlet for the refrigerant that opens into the refrigerant tank sections 6. An inlet portion of the refrigerant inlet header 9 has a cylindrical shape adapted for connection with the refrigerant passage 7, while the other end portion has a hollow configuration closed by a plug 13, as shown in FIG. 5. The endplate 11 is not formed with any port that opens into the one refrigerant tank section 6 of each refrigerant tube 1, and the other refrigerant tank section 6 is closed by the endplate 11.
Like the refrigerant inlet header 9, a refrigerant outlet header 14 is provided on the upper portion of the other side face of the heat exchanger. A connecting hole is bored through a side portion of the header 14. This hole is connected to a refrigerant outlet port in an endplate 15 by being fitted thereon. The outlet port is bored through the endplate 15 and opens into the refrigerant tank sections 6. An inlet portion of the refrigerant outlet header 14 has a cylindrical shape adapted for connection with the refrigerant passage 7, while the other end portion has a hollow configuration closed by a plug.
FIG. 6 is a view showing another example of the laminated heat exchanger, in which refrigerant tank sections are arranged on either side of a radiating laminated structure as a core section. Refrigerant tank sections 16, refrigerant inlet header 17, and refrigerant outlet header 18 of this heat exchanger are arranged in the same relation as those of the laminated heat exchanger shown in FIGS. 1 to 5. The laminated heat exchanger of this type may include a dimpled refrigerant passage 7 (not shown in FIG. 6) that are provided with no inner fins 8.
In this arrangement, the refrigerant is introduced through the refrigerant inlet header 9, flows into the refrigerant passage 7 through the inlet port 10, and exchanges heat with air in the passage 7. Then, the refrigerant is discharged through the refrigerant outlet header 14.
However, each conventional laminated heat exchanger described above, especially when used as an evaporator, is subject to the following problem. Immediately after the air conditioner, having the evaporator therein, is activated during its intermittent operation in which it is repeatedly activated and stopped in response to commands from a room-temperature control thermostat, the refrigerant flows in a large quantity through the refrigerant passage in the heat exchanger, though only for a short period of time. At this time, the refrigerant is introduced from the refrigerant inlet header 9 into the refrigerant tank sections 6 through the inlet port 10 of the endplate 11. As the refrigerant flows into each refrigerant tube 1, it suddenly changes its course 90.degree.. As the refrigerant flows into the tank sections 6 via the inlet port 10 in this manner, its flow direction is violently disturbed to cause a strong vortex. Under conditions combining a specific temperature, pressure, refrigerant flow rate, etc., pure tones may be produced in some cases.
FIG. 7 shows flows of the refrigerant in the refrigerant inlet header 9. As shown in FIG. 7, a large vortex causes a substantial turbulence in the region where the refrigerant runs against the plug 13, and the main current of the refrigerant flowing into the refrigerant tank sections 6 is biased to the area under the inlet port 10. Immediately after reactivation, moreover, the flow rate of the refrigerant increases to an extreme in some regions. In some cases, therefore, pure tones may be produced in the same manner as aforesaid.
The following is a description of pure tones produced by a heat exchanger. As compared with a pure tone, a sound (hereinafter referred to as "random sound") that has a certain frequency band covers a plurality of frequencies. If its level is high, therefore, a random sound is hardly distinguishable from background noises (vehicle noises, etc.), so that there is not a good possibility of its arousing a noise problem.
Undoubtedly, on the other hand, a pure tone has its peak at a specific frequency, so that it can be discriminated more frequently by the human ear than a random sound that has equal acoustic energy. This phenomenon depends on human auditory response, so that production of pure tones must be prevented in consideration of the quality of sound or tone, as well as the sound level.
The following is a description of the reason why pure tones are produced. If there is a stepped portion in a flow path, vortexes are produced on the rear-flow side of a flow, as shown in FIG. 8. These vortexes are not stable because they are in contact with no stepped portion. In consequence, a produced sound is not a tone that has a specific frequency, but a sound that has a certain range of frequency.
If a flow path has a groove, on the other hand, there is a stepped portion that can be touched by a vortex, as shown in FIG. 9, so that the vortex is stable. Thus, a produced sound is a pure tone that has a specific frequency.
Based on this principle of sound production, sounds are produced starting at a large number of groove-shaped gaps in the laminated heat exchanger shown in FIG. 4 that are structurally inevitable and are found by observing the structure of the evaporator and its gate pipe junctions.